Judges are cautioned not to take bribes, because bribery will cause even the wisest person to judge wrongly. The Sages relate an incident that underscores how the ties of affection created by receiving a gift from another person, even though it is not bribery at all, influence the recipient in a manner that he cannot control.

“You shall not take a bribe, as the bribe will blind the eyes of the wise” (Deuteronomy 16:19). Once the judge begins thinking of bribery, he becomes blind vis-à-vis the case, and he is unable to adjudicate it correctly.…

Rabbi Yishmael ben Elisha said: Come and see how severe bribery is. One time, a certain person came and brought me the first shearing of his sheep [one of the gifts given to a priest]. He had a case before a judge, and I was standing off to one side, and I said: If he advances such and such claim before the judge, he will win his case, and I was hoping for his victory. Even though he gave me only what was mine, as he was required by Torah law to give the wool to a priest, and it was not bribery, nevertheless my heart felt close to him as long as I was watching him. Even after he went to court [sometime after the court case], I asked whether he emerged victorious or not. This informs us how grave bribery is, as it blinds the eyes.

This matter may be inferred a fortiori: If in my incident, where he brought me what was mine and I took what was mine, I was hoping for his victory, with regard to one who takes a bribe, all the more so will he support the case of the one who bribed him. (Tanĥuma [Buber], Shofetim)